In various manufacturing and production environments, there is a need to control alignment between various layers of samples, or within particular layers of such samples. For example, in the semiconductor manufacturing industry, electronic devices may be produced by fabricating a series of layers on a substrate, some or all of the layers including various structures. The relative position of such structures both within particular layers and with respect to structures in other layers is relevant or even critical to the performance of completed electronic devices.
The relative position of structures within such a sample is sometimes called overlay. Various technology and processes for measuring overlay have been developed and employed with varying degrees of success. More recently, various efforts have been focused on utilizing radiation scatterometry as a basis for overlay metrology.
Certain existing approaches to determining overlay from scatterometry measurements concentrate on comparison of the measured spectra to calculated theoretical spectra based on model shape profiles, overlay, and film stack, and material optical properties (n, k dispersion curves), or comparison to a reference signal from a calibration wafer. In alternative approaches, various implementations of sub-optimal multi-cell targets have been employed. However, these approaches have numerous shortcomings, which the present invention seeks to overcome. The present invention discloses improved scatterometry overlay (SCOL) target structures and methods.